| Method for effecting the anaerobic biological decomposition of organsiloxanes -> Monitor Keywords |
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Method for effecting the anaerobic biological decomposition of organsiloxanesRelated Patent Categories: Chemistry: Molecular Biology And Microbiology, Process Of Utilizing An Enzyme Or Micro-organism To Destroy Hazardous Or Toxic Waste, Liberate, Separate, Or Purify A Preexisting Compound Or Composition Therefore; Cleaning Objects Or TextilesMethod for effecting the anaerobic biological decomposition of organsiloxanes description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070178577, Method for effecting the anaerobic biological decomposition of organsiloxanes. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to the anaerobic decomposition of linear or cyclic polyorganosiloxanes such as, for example, polydimethylsiloxane (PDMS) or organo-functional siloxanes, organosilanes, in particular organosilanols, and fragments formed from these compounds via chemical depolymerization. [0002] Annually, several 100 000 tons of polymers are produced on the basis of polydimethylsiloxane (PDMS), based on an --(Si--O--Si)-- repeating unit. A large part of these siloxanes passes into the environment during or after the use (textile industry, laundry detergent, paper industry, cosmetics, construction, pharmacy, agrochemicals, petrochemicals etc.). Siloxanes are polymers which do not occur naturally. To date, also, no biological processes are known which form or cleave an Si--C bond between a silicon atom and the carbon atom of a methyl group. Methods for the biological decomposition of siloxanes in wastewaters, e.g. in municipal sewage treatment plants or in wastewater treatment facilities of the chemical industry, in soils, sediments, sludges or other environmental compartments are not known. [0003] Gravier et al. (2003) summarize how siloxane polymers are chemically decomposed in the environment. No enrichment of the high-molecular-weight siloxanes occurs, but these are essentially decomposed by hydrolysis in aqueous or terrestrial habitats to form organosilanol-terminated oligomers. These organosilanols and low-molecular-weight PDMS fragments and also cyclic siloxanes evaporate into the atmosphere, where they are ultimately oxidized to silicate, CO.sub.2 and water by the hydroxyl radicals present there. [0004] A high-molecular-weight polyorganosiloxane is not water soluble. In aqueous systems or in wastewater, phase separation occurs. Polyorganosiloxane accumulates essentially on particulate constituents in the water or forms, owing to a specific weight <1.0 g/cm.sup.3, a siloxane film at the surface. Polyorganosiloxane, in sewage treatment plants, even if an aerobic biological state is present, is therefore neither destroyed nor decomposed, but ends virtually quantitatively in the solid phase of the sewage sludge. Studies of such sludges have shown that the high-molecular-weight siloxanes are there then depolymerized in on average 20-30 days (Gravier et al. 2003) and then as described pass into the atmosphere and are there oxidized. [0005] Grasset and Palla (U.S. Pat. No. 6,020,184) have described that decomposition of polymeric siloxane can also take place in aqueous systems. For this, an aqueous polyorgano-siloxane suspension is admixed with a biologically utilizable cosubstrate such as glucose and inoculated with a fungus of the genus Phanaerochaete or Aspergillus and incubated aerobically. Under these conditions, even in aqueous systems, in 60 days, up to 80% of the polymeric PDMS has decomposed. It is known that the fungi used do not first completely oxidize glucose, but produce organic acids. At the corresponding pHs of 2.5-4.5, acidic hydrolysis of the PDMS to give low-molecular-weight constituents takes place. Direct biological decomposition of the PDMS is not described. [0006] Volatile low-molecular-weight decomposition products of PDMS are principally finally oxidized in the atmosphere; although combined biological and chemical decomposition under aerobic conditions is described (Graiver et al. 2003), it is not of importance in practice, since the evaporation rate of volatile organosilicones is 2-20 times greater than the biological decomposition rate. Accumulation of low-molecular-weight organosilicones in soils and sediments which are close to the surface and well ventilated therefore does not take place, although in deeper sediment layers and non-ventilated soils, nevertheless, accumulation of such compounds can occur. [0007] It is an object of the present invention to provide a method by which a material comprising silicon-carbon single bonds, preferably polyorganosiloxanes, such as, for example, PDMS or organofunctional siloxanes, or organosilanes, in particular organosilanols, or fragments formed by chemical depolymerization thereof can be biologically decomposed. [0008] The object is achieved by a method which is characterized in that a mixture of a material comprising silicon-carbon single bonds and a microorganism population is incubated under anaerobic or microaerobic conditions with addition of an alternative electron acceptor. [0009] The material comprising silicon-carbon single bonds is preferably a material comprising polyorganosiloxanes, organofunctional siloxanes, organosilanes or fragments formed from these compounds. Preferably, the material is a liquid or a solid. [0010] The compounds which can preferably be decomposed by the inventive method are preferably compounds of the formulae (1 to 3) HO(SiR.sub.2O).sub.pH (1) where p.gtoreq.1, R.sub.3SiO(SiR.sub.2O).sub.qSiR.sub.3 (2) where q.gtoreq.0, (SiR.sub.2O).sub.r (3) where r=3-10, or a mixed polymer of units of the formulae HOR.sub.2SiO.sub.1/2, R.sub.3SiO.sub.1/2, R.sub.2SiO, RSi(OH)O, RSiO.sub.3/2 and HOSiO.sub.3/2, or an organosiloxane resin of units of the formula [R.sub.3SiO.sub.1/2] and [SiO.sub.4/2], which further comprise additional Si-bound OH groups, R, R.sub.2 and R.sub.3 each being able to be identical or different and a monovalent, linear or cyclic, branched or unbranched, if appropriate substituted, hydrocarbon radical. [0011] An alternative electron acceptor is taken to mean an electron acceptor except for oxygen. The alternative electron acceptor can be an organic compound or an inorganic compound. It serves to transfer the electrons taken up by the microorganism population in the oxidation of an Si--R bond (R being a monovalent organic radical, preferably a monovalent alkyl or aryl radical) and thus to enable the microorganism population to produce energy from substrate oxidation in the context of anaerobic respiration. [0012] Organic alternative electron acceptors are, for example, fumarate or succinate. Inorganic alternative electron acceptors are, for example, oxidized iron ions, sulfate or nitrate. Preferably, for the inventive method, use is made of sulfate or nitrate, particularly preferably nitrate. [0013] The alternative electron acceptor is present in the mixture preferably in a concentration of 0.1-100 mM. Particularly preferably, the electron acceptor is added in such a manner that it is present in a concentration of 1-100 mM. [0014] Microaerobic conditions are taken to mean conditions in which less than 5% of free or dissolved oxygen is present in the mixture. Preference is given to conditions in which less than 1% of free or dissolved oxygen is present in the mixture. Particular preference is given to conditions in which less than 250 ppm of free or dissolved oxygen is present in the mixture. [0015] Microaerobic or anaerobic conditions can be achieved, for example, by technical methods such as gas exchange or chemical consumption of residual oxygen. Preferably, microaerobic or anaerobic conditions are produced by oxygen present being consumed by the microorganism population present and the feed of further oxygen being suppressed. Particularly preferably, the microaerobic or anaerobic conditions are achieved by the inventive method being carried out in a closed vessel such as, for example, a digestion tower in a sewage treatment plant. [0016] The microorganism population is preferably a population such as is present in sewage sludge or in a sewage treatment plant or in a soil sediment. Preferably, it is a microorganism population which grows under anaerobic conditions, particularly preferably displays optimal growth under these conditions. [0017] In the inventive method, microorganism populations can be added externally, or microorganisms already present in the mixture (sewage sludge, soil etc.) can be used. [0018] The inventive method, in contrast to the method disclosed in U.S. Pat. No. 6,020,184, does not require any further oxidizable substrates (cosubstrates) such as, for example, carbohydrates, for example glucose. [0019] Preference is given to methods in which no oxidizable cosubstrates are added. Particular preference is given to those methods in which no cosubstrates are present in the batch and the batch therefore consists of said components. [0020] The method is preferably carried out at a temperature of 20.degree. C. to 80.degree. C., more preferably at a temperature of 30.degree. C. to 70.degree. C., in particular preferably at a temperature of 40.degree. C. to 60.degree. C. [0021] The incubation preferably proceeds over a period of 1 to 200 h, more preferably 10 to 150 h, in particular preferably 24 to 100 h. [0022] The inventive method is suitable for decomposing polyorganosiloxanes such as, for example, PDMS or organofunctional siloxanes, and organosilanes, in particular organosilanols, continuously (i.e. with permanent inflow of new substrate and simultaneous discharge of decomposed products) or batchwise (i.e. in a batch without further inflow of new substrate). [0023] In the inventive method, the polyorganosiloxanes or organosilanes can already have been prehydrolyzed upstream of the anaerobic decomposition by means of hydrolysis, e.g. by treatment with acid or base. [0024] The inventive method functions, for example, in a sewage treatment plant, in sediments or in other aquatic or terrestrial compartments. For instance, the inventive method can be used, for example, in an anaerobic stage in a wastewater treatment plant, or it can be used to decompose polyorganosiloxane or organo-silane or fragments formed therefrom via chemical depolymerization present in terrestrial or aquatic low-oxygen or oxygen-free compartments. Continue reading about Method for effecting the anaerobic biological decomposition of organsiloxanes... 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